Self-centering braze assembly

ABSTRACT

Braze and electrode wire assemblies, e.g., used with an implantable microstimulator, include a wire welded in the through-hole of an electrode, which electrode is brazed to a ceramic case that is brazed to a metal ring that is welded to a metal can. The braze joints are step or similar joints that self-center the case, provide lateral support during braze assembly, and provide increased surface area that prevents braze material from exuding from the joints. The end of the ceramic case that is brazed to the metal ring need not be specially machined. The shell has a reference electrode on one end and an active electrode on the other, and is externally coated on selected areas with conductive and non-conductive materials.

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/392,475, filed Jun. 28, 2002, which applicationis incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to braze assemblies and more particularlyto self-centering braze assemblies of ceramic and metallic materials forapplications such as medical devices, electrical connectors, electronicspackages, and structural components.

BACKGROUND OF THE INVENTION

Many products made of different materials with different properties aremanufactured by sealing the different materials together. A seal betweentwo different materials can be produced by welding, gluing, brazing, orsimilar processes. Brazing is the process of soldering two materialswith different properties, such as ceramic and metal, together using ahard solder with a relatively high melting point. One can create a verystrong and lasting seal between two different materials by employing thebraze materials and methods described in the prior art. Many productsbenefit from brazing, including medical devices such as implantablemicrostimulators. A strong hermetic seal is required between ceramic andmetallic materials of the outer case of some microstimulators.

Implantable microstimulators known as Bion® devices are characterized bya small, cylindrical housing which contains electronic circuitry forproducing electric currents between spaced electrodes. Themicrostimulators are implanted proximate to the target tissue, and thecurrents produced by the electrodes stimulate the tissue to reducesymptoms or otherwise provide therapy for various disorders.Microstimulators often include valuable electronic circuitry, batteries,and other components that must be hermetically sealed within a securecase in order to protect the inner components of the microstimulatorfrom damage by surrounding tissue and in order to protect a patient fromharm caused by a malfunctioning microstimulator.

Radio-frequency powered and battery powered microstimulators aredescribed in the art. See, for instance, U.S. Pat. No. 5,193,539(“Implantable Microstimulator); U.S. Pat. No. 5,193,540 (“Structure andMethod of Manufacture of an Implantable Microstimulator”); U.S. Pat. No.5,312,439 (“Implantable Device Having an Electrolytic StorageElectrode”); U.S. Pat. No. 6,185,452 (“Battery-Powered PatientImplantable Device”); U.S. Pat. Nos. 6,164,284 and 6,208,894 (bothtitled “System of Implantable Device for Monitoring and/or AffectingBody Parameters”). The '539, '540, '439, '452, '284, and '894 patentsare incorporated herein by reference in their entirety.

Microstimulators that prevent and/or treat various disorders associatedwith prolonged inactivity, confinement or immobilization of one or moremuscles are taught, e.g., in U.S. Pat. No. 6,061,596 (“Method forConditioning Pelvis Musculature Using an Implanted Microstimulator”);U.S. Pat. No. 6,051,017 (“Implantable Microstimulator and SystemsEmploying the Same”); U.S. Pat. No. 6,175,764 (“ImplantableMicrostimulator System for Producing Repeatable Patterns of ElectricalStimulation”); U.S. Pat. No. 6,181,965 (“Implantable MicrostimulatorSystem for Prevention of Disorders”); U.S. Pat. No. 6,185,455 (“Methodsof Reducing the Incidence of Medical Complications Using ImplantableMicrostimulators”); and U.S. Pat. No. 6,214,032 (“System for Implantinga Microstimulator”). The techniques described in these additionalpatents, including power charging techniques, may also be used with thepresent invention. The '596, '017, '764, '965, '455, and '032 patentsare incorporated herein by reference in their entirety.

The various types of microstimulators known in the art, and otherproducts in other arts, often employ brazing materials and methods tocreate hermetic seals for the cases that house the inner components ofsuch devices. For example, U.S. Pat. No. 6,221,513, which patent isincorporated herein by reference in its entirety, describes methods forhermetically sealing ceramic to metallic surfaces and assemblies thatincorporate ceramic to metallic seals. The '513 patent discloses abrazed butt joint, a brazed bevel joint, and a braze joint between ametal end cap and a ceramic open-ended cylinder. Another example,International Publication No. WO 00/56394, which publication isincorporated herein by reference in its entirety, describes a ceramiccase assembly for a microstimulator. The '394 publication discloses abrazed butt joint, a brazed internal step joint for self-jigging, and abraze joint between a metal end cap and a ceramic open-ended cylinder.Yet another example, International Publication No. WO 00/56677, whichpublication is also incorporated herein by reference in its entirety,describes both a self-jigging bevel joint and a self-jigging internalstep joint for a metal-ceramic braze bond. In a final example, U.S. Pat.No. 4,991,582, which patent is also incorporated herein by reference inits entirety, discloses a metal to machined ceramic braze bond using aself-jigging step joint.

Although the various types of hermetic seals and braze joints known inthe art may be useful for microstimulators and other products,significant improvements upon these seals and joints are still possibleand desirable, particularly relative to a braze joint creating a strongand safe hermetic seal that can be successfully produced on a consistentbasis and in a cost effective manner.

For example, the '513 patent and the '394 and '677 publications arelikely to suffer from the undesirable effects of braze material thatexudes from the joint to the outer surface of a device case duringassembly. When braze material exudes, during assembly, to the outersurface of the case, the material cools after the brazing process iscomplete to create a sharp metallic burr, e.g., on the outside surfaceof the device case. This burr, if not removed, could cause significantdiscomfort, damage, and injury to a patient when the microstimulator isimplanted. Yet, removing the dangerous burr after braze assembly usingany technique—including chipping, sanding, shaving, laser cutting orother method—is certain to increase the manufacturing time and cost andis very likely to compromise the strength of the braze bond.

Further, the '582 patent discloses a step joint between a metal memberand a ceramic case, which ceramic case is machined to include a stepthat specifically fits in communication with the metal member at thejoint. Machining a ceramic case often leaves residual cracks and weakensthe case, especially where the wall of the ceramic case is thin.

Therefore, a need exists for a braze joint assembly that improves uponthe prior art by providing a strong ceramic case at the braze joint anda means for inhibiting braze material exudation.

SUMMARY OF THE INVENTION

The present invention addresses the above and other needs by providing aself-centering braze assembly for hermetically sealing the metal andceramic materials of various products, e.g., a Bion® or othermicrostimulator. The present invention also describes the method ofassembling and brazing the materials used to create the hermetic seal ofa self-centering braze assembly. The self-centering braze assemblyincludes increased surface area at the braze joint. This increasedsurface area permits the use of an adequate amount of braze materialthat is necessary to create a strong braze joint. At the same time, theincreased surface area inhibits braze material from exuding from thebraze joint. Further, the self-centering braze assembly includes aflange on a metal ring that encompasses the external, orouter-circumferential, surface of the ceramic case at the braze joint.This flange acts as a dam that inhibits braze material from exuding fromthe braze joint. Further, the present invention includes a ceramic casethat need not be machined at the braze joint and is therefore strongerat the braze joint.

The self-centering braze assembly of the present invention is made frombiocompatible, hermetically-sealable material. A first braze assembly ofthe present invention includes a ceramic case brazed to a metal ringusing braze material. The braze material is a titanium/nickel alloy orsimilar alloy capable of adhering to and creating a strong metal bondbetween ceramic and metal during a brazing process. The metal ring ismanufactured using titanium, or other biocompatible metal, and includesan external step joint, external step/bevel joint, or other joint withat least one external flange. Braze, ceramic, and metal materials andbrazing methods useful with the present invention include thosematerials and methods known in the art, such as those disclosed in U.S.Pat. No. 6,221,513, and International Publication Nos. WO 00/56677 andWO 00/56394.

The at least one external flange communicates with the outercircumference of the ceramic case. The at least one external flange andstep, or other surface, of the metal ring are long enough to provideadequate surface area in contact with the ceramic case, so as to preventbraze material from exuding from the joint along the outercircumferential surface of the joint while allowing an appropriateamount of braze material to be applied to the joint in order to create astrong bond. Both the external flange communicating with the outersurface of the ceramic case and the increased surface area of thepresent invention are significant improvements over the prior art,including the '513 patent and the '394 and '677 publications. The '513patent and the '394 and '677 publications fail to teach, inter alia, abraze assembly employing both an external flange that communicates withthe outer diameter of a ceramic case and also a flange and step or otherjoint with adequate or increased surface area.

The end of the ceramic case that communicates with the metal ring neednot be specially machined to be able to form a mutually-butted stepjoint, or other mutual joint, with the metal ring. In other words, theend of the ceramic case that communicates with the metal ring need notbe cut, shaped, or machined as a step, bevel, or other similar surface.Rather, the end of the ceramic case that communicates with the metalring is a butted end. The butted end of the ceramic case is asignificant improvement over U.S. Pat. No. 4,991,582 which uses amachined ceramic case that is susceptible to residual cracks thatultimately lead to a weakened braze joint. The present invention, byproviding a ceramic case with a butted end, is capable of employingceramic cases with very thin walls, e.g., approximately 0.010 inchesthick.

The present invention also includes a second braze assembly, whichsecond braze assembly includes a ceramic close-ended can, brazematerial, and an electrode. A small hole is defined in the end of asubstantially closed end of the ceramic can, the inner circumferentialsurface of which communicates with an outer circumferential surface of apin of the electrode. A bottom surface of the electrode communicateswith a bottom surface of the substantially closed end of the ceramiccan, between which surfaces the braze material has adequate surface areato melt and bond without exuding from the exterior circumference of thejoint. The increased surface area of the present invention is asignificant improvement over the prior art, including InternationalPublication No. WO 090/56394, which describes a braze assembly between ametal end cap and a ceramic open-ended cylinder, not a ceramicclose-ended can. The width of the wall of the ceramic open-endedcylinder provides insufficient surface area which, when placed incommunication with the metal end cap, allows braze material to exude andestablishes a relatively weak braze bond.

The present invention also includes a through-hole assembly and methodof assembly for attaching a wire to a capacitor and an electrode.

Methods of manufacturing/assembling a hermetically sealed housing forthe internal components of a microstimulator are described herein. Alsodescribed herein are methods and materials for externally coating thehermetically sealed cylindrical housing to protect the internalcomponents.

Embodiments described herein may include some or all of the itemsmentioned above. Additional embodiments will be evident upon furtherreview of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will be moreapparent from the following more particular description thereof,presented in conjunction with the following drawings wherein:

FIG. 1A is a cross-sectional view of a Bion® shell of the presentinvention;

FIG. 1B is an end view of the Bion® shell of FIG. 1A;

FIG. 2A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal band, a high temperature brazepreform in the shape of a ring, and a ceramic case before assembly;

FIG. 2B is a cross-sectional view of the metal band, the hightemperature braze preform, and the ceramic case of FIG. 2A aligned witha cylinder during assembly;

FIG. 2C is a cross-sectional view of the metal band and ceramic case ofFIG. 2A after assembly;

FIG. 3A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal or metal alloy cylinder, a ceramiccylinder, and a braze preform before assembly;

FIG. 3B is a cross-sectional view of the metal or metal alloy cylinderand the ceramic cylinder of FIG. 3A forming a self-jigging bevel jointafter assembly;

FIG. 4A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal or metal alloy cylinder, a ceramiccylinder, and a braze preform before assembly;

FIG. 4B is a cross-sectional view of the metal or metal alloy cylinderand the ceramic cylinder of FIG. 4A forming a self-jigging internal stepjoint after assembly;

FIG. 5A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal band, a metal braze material, anda ceramic sleeve with a machined flange before assembly;

FIG. 5B is a cross-sectional view of the metal band and the ceramicsleeve with a machined flange of FIG. 5A after assembly;

FIG. 6A is a cross-sectional view of the present invention of a metalring with an external flange, a braze material, and a ceramic can beforeassembly;

FIG. 6B is a cross-sectional view of the metal ring and the ceramic canof FIG. 6A forming a self-jigging external step joint after assembly;

FIG. 6C represents an actual 200:1 enlarged view of a cross-section ofthe external step joint after assembly;

FIG. 7A is a cross-sectional view of the present invention of a metalring with internal and external flanges, a braze material, and a ceramiccan before assembly;

FIG. 7B is a cross-sectional view of the metal ring and the ceramic canof FIG. 7A forming a u-joint after assembly;

FIG. 8A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of an open-ended ceramic cylinder, a hightemperature braze preform, and a metal end cap before assembly;

FIG. 8B is a cross-sectional view of the open-ended ceramic cylinder andmetal end cap of FIG. 8A after assembly;

FIG. 9A is a cross-sectional view of the present invention of aclose-ended ceramic can, a braze material, and an electrode beforeassembly;

FIG. 9B is a cross-sectional view of the close-ended ceramic can, thebraze material, and the electrode of FIG. 9A after assembly;

FIG. 9C represents an actual 50:1 enlarged view of a cross-section ofthe braze joint assembly after assembly;

FIG. 10 is a cross-sectional view of the present invention of a Bion®case with a parylene coating;

FIG. 11 is a perspective view of a completed braze assembly and atitanium wire;

FIG. 12 is a perspective view of a completed braze assembly and theinner components of a microstimulator housed in a carrier;

FIG. 13 is a perspective view of a microstimulator before finalassembly;

FIG. 14 is a perspective view of a microstimulator horizontally housedin a carrier;

FIG. 15 is a perspective view of a microstimulator vertically housed ina carrier; and

FIG. 16 is a perspective view of a microstimulator after final assembly.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

The present invention may be used with numerous devices. Such devicesmay include implantable medical devices, such as microstimulators.However, as will be understood by those of skill in the art, the presentinvention may be used with other types of devices. The exemplary medicaldevice that will be used herein to describe the systems and methods ofthe present invention is a small, implantable stimulator, and moreparticularly a microstimulator known as a Bion® microstimulator.

The Bion® microstimulator has a substantially cylindrical shape (othershapes are possible) and at least portions of it are hermetically sealedusing the methods and structure of the present invention. The Bion®microstimulator includes a processor and other electronic circuitry thatallow it to generate stimulus pulses that are applied to a patientthrough electrodes in accordance with a program that may be stored, ifnecessary or desired, in programmable memory.

The Bion® microstimulator manufactured in part by the present inventionincludes internal and external components. The internal components ofthe Bion® microstimulator are encompassed by a hermetically sealed metaland ceramic case, which case is welded and brazed together using theself-centering braze assembly structures and methods of the presentinvention.

FIG. 1A is a cross-sectional view of a Bion® microstimulator shell 800assembled using the present invention. The shell 800 encapsulates theinternal components of the Bion® microstimulator. The shell 800 is anexemplary hermetically-sealed housing which consists of, for instance,two cylindrical cases, or cans: a metal or metal alloy case, or can, 213and a ceramic case, or can, 215. Alternative materials and shapes forthe shell may also be used. Alternative materials include stabilizedzirconia, partially stabilized zirconia, yttria-stabilized zirconia,tretragonal zirconia, magnesia-stabilized zirconia, ceria-stabilizedzirconia, calcia-stabilized zirconia, alumina, silicon nitride, siliconcarbide, titanium carbide, tungsten carbide, titanium nitride, siliconaluminum oxy-nitride (sialon), graphite, titanium di-boride, boroncarbide, molybdenum disilicide, copper, titanium-niobium,titanium-tantalum, molybdenum, and zirconium.

The metal or metal alloy case 213 may be manufactured from an alloy withlow interstitial defects, e.g., a titanium 6/4 alloy, and may have awall approximately 0.003 inches thick. The case 213 may be precisionscrew machined from rod stock and preferably includes a closed endmachined design that eliminates the need to laser weld an end cap at theend of the case 213.

A connector, or metal ring, 236 made from metal or metal alloy, e.g.,titanium 6/4 alloy, is brazed with a titanium nickel alloy (or othersuitable material) to the ceramic case 215. During the brazing process,the braze assembly (consisting of the ceramic case 215, the connector236, and the titanium nickel alloy) is gradually heated in a vacuumuntil the titanium nickel alloy forms a liquidus. Then the brazeassembly is gradually cooled until the braze material forms a solidus.

Titanium nickel alloys used with the present invention includeproportions of titanium to nickel similar to those disclosed in theprior art, including U.S. Pat. No. 6,221,513 and InternationalPublication Nos. WO 00/56394 and WO 00/56677. The connector 236 has aninternal flange 236A and an outside flange 236B (also referred to hereinas “external flange” or “exterior flange”), which flanges serve to“self-center” the braze assembly. The internal flange 236A and theconnector 236 are laser welded, or otherwise permanently attached, tocase 213. The connector 236 may be manufactured from an alloy with lowinterstitial defects and may have an external flange 236B approximately0.003 inches thick. The external flange 236B is long enough to supply anadequate surface area in which the connector 236 is brazed to theceramic case 215 using an amount of braze material adequate to create astrong hermetic seal without permitting the braze material to exude fromthe braze joint to the exterior surface of the shell 800. The externalflange 236B also serves to wick surplus braze material away from theinner diameter of the shell 800 as a result of the surface tension ofthe braze material.

The ceramic case, or can, 215 has a wall thickness at the braze joint ofapproximately 0.010 inches and may be manufactured from solid sinteredstock. The ceramic case, or can, 215 may instead be manufactured from anear net shape sintered can where the outer diameter of can 215 is heldto a tolerance of +/−0.0002 inches in order to ensure that braze jointstrength remains consistent. The ceramic can 215 has a substantiallyclosed-end 802 defining a hole with a relatively narrow diameter.

Before inserting the internal components and before securing the matingends, conductive silicone adhesive 238, as shown in FIG. 1A, may beapplied to the inside end of the ceramic shell as well as to the insideend of the titanium shell. A molecular sieve moisture getter materialmay also be added to areas 235A, 235B, and 235C at appropriate momentsduring the assembly of the internal components, but preferably beforethe brazing process is initiated. The moisture getter material serves toabsorb moisture that might otherwise accumulate on sensitive internalcomponents during brazing or welding processes.

A self-centering button electrode 22 is made from titanium 6/4 or othersuitable material and is plated with a 3 micron iridium coating or othersuitable conductive coating. A titanium/nickel alloy 240 or othersuitable material is used to braze the button electrode 22 to theceramic case 215. The electrode 22 has a pin 801 with a relativelynarrow diameter. The outer circumferential surface of the pin 801communicates with the inner surface of the closed end 802 of the can215.

FIG. 1B is an end view of the Bion® microstimulator shown in FIG. 1A.The self-centering button electrode 22 with a spiral groove 324 cut intoits surface is made from titanium 6/4 or other suitable material and isplated with an iridium coating or other suitable conductive coating. Thespiral groove 324 is cut into a stimulating surface 322 of the electrode22. The spiral groove 324 is just one example of groove shapes that maybe used; other shapes and patterns, such as a cross hatch pattern, aconcentric ring pattern, a parallel line pattern, or other pattern thatincreases the surface area of the stimulating surface 322 mayalso/instead be used on button shaped electrodes, sphere shapedelectrodes, or otherwise shaped electrodes. The groove 324 increases theconductive surface area 322 of the electrode 22.

The sharp edges in the groove 324 force a more homogeneous currentdistribution over the surface 322 and decrease the chances of electrodecorrosion over time. The corrosion effect which may affect the electrode22 is also known as biofouling, which is the gradual accumulation ofbacteria on the surface of the electrode 22 once immersed in body fluid.When current is injected into body fluids, an electrochemical reactionoccurs, producing large amounts of current density, which can contributeto the accumulation of bacteria. The spiral groove 324 or similar groovehelps reduce the current density along the sharp groove edges. A toolmade in the shape of a trapezoid or similar shape is used to cut thegroove 324 into a spiral or other shape. Other methods of cutting thegroove 324 may be used, e.g., ion beam etching.

The braze, ceramic, and metal materials and the brazing methods known inthe art, such as those disclosed in U.S. Pat. No. 6,221,513, andInternational Publication Nos. WO 00/56677 and WO 00/56394, may be usedwith the present invention. The '513 patent provides helpful examples ofmethods for brazing the materials of the present invention.

FIGS. 2A to 5B portray various braze joints, before and after assembly,that are similar to those disclosed by the prior art.

FIG. 2A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal band 803, a high temperature brazepreform 804 in the shape of a ring, and a ceramic case 805 beforeassembly. FIG. 2B is a cross-sectional view of the metal band 803, thehigh temperature braze preform 804, and the ceramic case 805 of FIG. 2Aaligned with a cylinder 806 during assembly. FIG. 2C is across-sectional view of the metal band 803 and the ceramic case 805 ofFIG. 2A after assembly. Because the metal band 803 and the ceramic case805 form a butt joint, and because this joint provides a minimal amountof surface area to which braze material may bond, the braze preform 804melts during assembly and often exudes from the joint and cools afterassembly to form a sharp ridge 807 of braze material along the exteriorsurface of the joint. The sharp ridge 807 should not be allowed toremain on the exterior surface of any consumer product, especially animplantable medical device. Permitting the sharp ridge 807 of metallicmaterial to remain on the outer case of an implantable medical devicewould expose a patient to unnecessary danger. Therefore, it is importantto remove the sharp ridge 807. Unfortunately, removing the sharp ridge807 by machining or other process is certain to add time and expense tothe assembly procedure and is very likely to weaken the braze joint as aresult. An improvement upon the braze joint of FIGS. 2A to 2C wouldprevent the sharp ridge 807 from forming during the braze assemblyprocess. Such an improvement is provided by the present invention.

Further, the butt joint of FIGS. 2A to 2C lacks substantial lateralsupport needed both during and after assembly. During assembly, themetal band 803 and the ceramic case 805 may be compressed towards eachother with tremendous pressure. A substantial amount of pressure isdesired to create a very strong braze joint. However, the butt jointassembly of FIGS. 2A to 2C likely lacks the lateral support necessary toprevent the assembly from buckling under a preferred amount of pressurewithout the aid of a support member such as a cylinder 806. Further, thebutt joint assembly of FIGS. 2A to 2C may lack adequate lateral supportto maintain a strong braze for the life and use of the product. Anotherimprovement upon the butt joint of FIGS. 2A to 2C would provide astructural joint with more lateral support than a butt joint. Such animprovement is provided by the present invention.

FIG. 3A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal or metal alloy cylinder 808, aceramic cylinder 809, and a braze preform 810 before assembly. FIG. 3Bis a cross-sectional view of the metal or metal alloy cylinder 808 andthe ceramic cylinder 809 of FIG. 3A forming a self-jigging bevel jointafter assembly. Because the metal or metal alloy cylinder 808 and theceramic cylinder 809 form a bevel joint, and because this joint onlyprovides slightly more surface area for braze material than a buttjoint, the braze preform 810 melts during assembly and often exudes fromthe joint and cools after assembly to form a sharp ridge 811 of brazematerial along the exterior surface of the joint. The sharp ridge 811should not be allowed to remain on the exterior surface of any consumerproduct, especially an implantable medical device. Permitting the sharpridge 811 of metallic material to remain on the outer case of animplantable medical device would expose a patient to unnecessary danger.Therefore, it is important to remove the sharp ridge 811. Unfortunately,removing the sharp ridge 811 by machining or other process is certain toadd time and expense to the assembly procedure and is very likely toweaken the braze joint as a result. An improvement upon the braze jointof FIGS. 3A and 3B would prevent the sharp ridge 811 from forming duringthe braze assembly process. Such an improvement is provided by thepresent invention.

Further, the bevel joint of FIGS. 3A and 3B lacks substantial lateralsupport needed both during and after assembly. During assembly, themetal or metal alloy cylinder 808 and the ceramic cylinder 809 may becompressed towards each other with tremendous pressure. A substantialamount of pressure is desired to create a very strong braze joint.However, the bevel joint assembly of FIGS. 3A and 3B likely lacks thelateral support necessary to prevent the assembly from buckling under apreferred amount of pressure. Further, the bevel joint assembly of FIGS.3A and 3B may lack adequate lateral support to maintain a strong brazefor the life and use of the product. Another improvement upon the brazejoint of FIGS. 3A and 3B would provide a structural joint with morelateral support than a bevel joint. Such an improvement is provided bythe present invention.

FIG. 4A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal or metal alloy cylinder 812, aceramic cylinder 813, and a braze preform 814 before assembly. FIG. 4Bis a cross-sectional view of the metal or metal alloy cylinder 812 andthe ceramic cylinder 813 of FIG. 4A forming a self-jigging internal stepjoint after assembly. The self-jigging internal step joint is formedusing the metal or metal alloy cylinder 812 which has a step with aninternal flange 815. The internal flange 815 adjoins the interiorsurface of the ceramic cylinder 813.

The internal step joint of FIGS. 4A and 4B provides more lateral supportand more surface area than the bevel and butt joints of FIGS. 2A to 3B.However, because the metal or metal alloy cylinder 812 and the ceramiccylinder 813 form an internal step joint with no external flange, thebraze preform 814 melts during assembly and often exudes from the jointand cools after assembly to form a sharp ridge 816 of braze materialalong the exterior surface of the joint. The sharp ridge 816 should notbe allowed to remain on the exterior surface of any consumer product,especially an implantable medical device. Permitting the sharp ridge 816of metallic material to remain on the outer case of an implantablemedical device would expose a patient to unnecessary danger. Therefore,it is important to remove the sharp ridge 816. Unfortunately, removingthe sharp ridge 816 by machining or other process is certain to add timeand expense to the assembly procedure and is very likely to weaken thebraze joint as a result. An improvement upon the internal step joint ofFIGS. 4A and 4B would prevent the sharp ridge 816 from ever formingduring the braze assembly process. Such an improvement is provided bythe present invention.

FIG. 5A is a cross-sectional view of an assembly similar to thatdisclosed by the prior art of a metal band 817, a metal braze material818, and a ceramic sleeve 819 with a machined flange 820 beforeassembly. FIG. 5B is a cross-sectional view of the metal band 817 andthe ceramic sleeve 819 with a machined flange 820 of FIG. 5A forming adouble step joint after assembly. The joint of FIGS. 5A and 5B providesincreased surface area 821 for braze material, which may permit a brazejoint to form without braze material exuding to the exterior 822 of thejoint.

Although FIGS. 5A and 5B provide a joint with both increased surfacearea and the lateral support of a step-type joint, the jointunfortunately includes a machined ceramic member that is likely toresult in a weak joint, especially where the ceramic member is thin. Themachined flange of 820 is formed by machining the end of the ceramicsleeve 819. Machining a ceramic case often leaves residual cracks andweakens the case, especially where the wall of the ceramic case is thin,e.g., less than a few millimeters in thickness. A joint created using aceramic case with a machined flange that is likely to crack or weaken isunacceptable for use with implantable medical devices or other devicesin which a user places her trust. An improvement upon the double stepjoint of FIGS. 5A and 5B would avoid using a ceramic member with amachined flange to form the joint. Such an improvement is provided bythe present invention.

FIGS. 6A to 7B represent embodiments of the present invention, the novelstructures of which successfully overcome many of the difficultiesencountered by the prior art by providing adequate surface area andlateral support in a braze joint with a ceramic member that need not bemachined. FIG. 6A is a cross-sectional view of the present invention ofa connector or metal ring 236 with an external flange 236B, anickel-titanium braze material 825, and a ceramic can 215 with a formedend 827 before assembly. The formed end 827 need not be machined asshown in the prior art. In other words, after the can 215 is initiallyformed, the formed end 827 need not be cut or otherwise modified in amanner that increases the likelihood of residual cracks forming in thecan 215. The formed end 827 may be any shape that forms a successfulbraze joint of the present invention. The braze material 825 can be anytype of braze material suitable for brazing metal to ceramic material.In one embodiment, nickel and titanium sheets are placed on top of eachother and rolled together during manufacturing. Later, the washer-shapedrings may be cut out to form the braze material 825.

FIG. 6B is a cross-sectional view of the metal ring 236 and the ceramiccan 215 of FIG. 6A forming a self-jigging external step joint afterassembly. External flange 236B, fitting snugly around the exteriorcircumferential surface of the formed end 827 of ceramic can 215,successfully serves to self-center the metal ring 236, the brazematerial 825, and the ceramic can 215 during assembly. External flange236B further acts as a dam to prevent the braze material 825 fromexuding to the exterior surface 828 of the joint.

Further, the surface area of the external step joint formed between themetal ring 236 and the ceramic can 215 provides adequate surface areafor a sufficient amount of the braze material 825 to form a strong brazebond without exuding from the joint. The surface tension of the nickeltitanium braze material 825 and the design of the joint serve to wickthe braze material away from the inner diameter of the shell 800 towardthe outer surface of the shell 800. However, because the presentinvention provides an increase surface area along which the brazematerial 825 may bond, an adequate amount of the braze material 825 isnot wicked so far as to exude to the outer or inner surface of the shell800. Even further, the step joint formed using the external flange 236Bof the metal ring 236 provides adequate lateral support for the jointcomponents to be assembled without the need for auxiliary componentsthat provide additional lateral support. By eliminating the need forauxiliary components, the present invention reduces the amount of time,materials, and complexity of the braze joint assembly process.

FIG. 6C represents an actual 200:1 enlarged view of a cross-section ofthe braze joint after assembly. The approach of FIGS. 6A and 6B has beentested and the actual results are portrayed in FIG. 6C. FIG. 6C showsthe metal ring 236 with the external flange 236B successfully brazed tothe ceramic can 215 using the braze material 825. The braze material825, after melting and cooling during the braze process, is spreadrelatively evenly along the entire surface area between the metal ring236 and ceramic can 215, forming a strong braze bond. The braze material825 has not exuded beyond the end of the external flange 236B. Byovercoming many of the challenges experienced in various teachings ofthe prior art in a single design, the present invention is a “smallstep” joint that represents a “giant leap” over the prior art.

FIG. 7A is a cross-sectional view of another embodiment of the presentinvention of a metal ring 829 with internal and external flanges 830, abraze material 831, and a ceramic can 832 with a formed end 833 beforeassembly. FIG. 7B is a cross-sectional view of the metal ring 829 andthe ceramic can 832 of FIG. 7A forming a u-joint after assembly. Theembodiment of FIGS. 7A and 7B enjoys benefits of the structure of theembodiment shown in FIGS. 6A to 6C, namely: a metal ring 829 having astepped end with an external flange 830 and a ceramic can 832 with aformed end 833. The embodiment of FIGS. 7A and 7B adds an internalflange 830A to the end of the metal ring 829 to present a potentialimprovement to the embodiment of FIGS. 6A to 6C and to illustrate thatnumerous other embodiments of the present invention are possible withoutexceeding the scope of the present invention as defined in the claims.The embodiments could include step joints, step-bevel joints, step-curvejoints, and other variously configured joints with at least one externalflange on the end of the metallic member and a formed end on the ceramicmember.

FIGS. 8A and 8B portray a braze joint, before and after assembly, thatis similar to a braze joint disclosed by the prior art. FIG. 8A is across-sectional view of an assembly similar to that disclosed by theprior art of an open-ended ceramic cylinder 834, a high temperaturebraze preform 835, and a metal end cap 836 before assembly. The metalend cap 836 has a pin with a broad diameter 837 that results in arelatively narrow braze joint surface area 838.

FIG. 8B is a cross-sectional view of the open-ended ceramic cylinder 834and metal end cap 836 of FIG. 8A after assembly. As a result of the pinwith a broad diameter 837 and the narrow braze joint surface area 838 ofthe end cap 836, the braze preform 835 often melts during braze assemblyand exudes out of the braze joint to form a sharp metal ridge 839 alongthe exterior surface of the braze joint. As mentioned earlier, the sharpmetal ridge 839 is dangerous and should be removed. However, machiningthe sharp metal ridge 839 is often difficult and expensive, and islikely to weaken the braze joint. An improvement upon the braze joint ofFIGS. 8A and 8B would prevent the sharp metal ridge 839 from formingduring the assembly process. Such an improvement is provided by thepresent invention.

FIGS. 9A to 9C represent embodiments of the present invention, the novelstructures of which successfully overcome many of the difficultiesencountered by the prior art, as exemplified in FIGS. 8A and 8B, byproviding surface area adequate to create a strong braze joint whilepreventing braze material from exuding from the joint.

FIG. 9A is a cross-sectional view of the present invention of a ceramiccan 215 with a closed end 845, a braze material 240, and an electrode 22before assembly. The electrode 22 has a hollow pin with a narrowdiameter 801 that results in a relatively broad braze joint surface area844.

FIG. 9B is a cross-sectional view of the ceramic can 215 with the closedend 845, the braze material 240, and the electrode 22 of FIG. 9A afterassembly. The pin 801 fits snugly into a hole in the end of the ceramiccan 215. The closed end 845 adjoins the joint surface area 844 toprovide a relatively broad surface area along which the braze material240 forms a strong bond without exuding from the joint. The closed end845 also provides greater support (than would an open end) againstpressure along the axis of the braze joint assembly when the ceramic can215 and the electrode 22 are compressed.

FIG. 9C represents an actual 50:1 enlarged view of a cross-section ofthe braze joint after assembly. The approach of FIGS. 9A and 9B has beentested and the actual results are portrayed in FIG. 9C. FIG. 9C showsthe closed end 845 of the ceramic can 215 successfully brazed to theelectrode 22 using the braze material 240. The braze material 240, aftermelting and cooling during the braze process, is spread relativelyevenly along the entire surface area between the ceramic can 215 and theelectrode 22, forming a strong braze bond. The braze material 240 hasnot exuded substantially beyond the end of the electrode 22. Less brazematerial 240 and/or less compression force between electrode 22 andceramic can 215 may be applied in order to limited the distance that thebraze material 240 is able to travel towards the exterior edge of thebraze joint while creating an adequately strong braze bond.

FIG. 10 is a cross-sectional view of the Bion® microstimulator shell 800of the present invention as shown in FIG. 1A with a parylene coating850. A type C parylene or other suitable insulation coating 850 isapplied to the exterior surface of shell 800 by standard masking andvapor deposition processes. The zirconia ceramic case is left exposed inarea 248 and an iridium electrode 24 is shown on an end 242 of the case213. FIG. 10 also shows two exemplary braze assemblies of the presentinvention as previously described. The braze assembly of FIGS. 6A to 6Cis shown at braze assembly 851. The braze assembly of FIGS. 9A to 9C isshown at braze assembly 852.

FIG. 11 is a perspective view of a completed braze assembly 855 and atitanium wire 856. The completed braze assembly 855 includes the metalring 236 brazed to the ceramic can 215, which in turn is brazed to anelectrode 857 with a feed-through hole that has been drilled orotherwise formed or created through the center of the electrode 857. Theelectrode 857 is made of machined titanium or other conductive material.The center core of the electrode 857 through which the feed-through holeis drilled is preferably thin enough to allow a small diameter drill bitto drill a small diameter hole through the entire core without breakingor overheating the drill bit.

Before the titanium wire 856 is threaded through the braze assembly 855,and end of the titanium wire 856 is bent (or otherwise prepared, e.g.,with a clip, ball, or other structure or bend capable of the samefunction) to form an elbow 858, so as to prevent the wire from slidingcompletely through the braze assembly 855 during threading. After thebraze assembly 855 is completely assembled with the electrode 857, theend of the titanium wire 856 opposite the elbow 858 end is threadedthrough the core of the braze assembly 855. The wire 856 may be threadedfrom either end of assembly 855, but is preferably threaded beginning atthe electrode 857 end. After the titanium wire 856 is threaded throughthe braze assembly 855, the end of the wire 856 that is opposite theelbow 858 end is bent to form a u-loop 859 or other substantiallysimilar shape.

FIG. 12 is a perspective view of a completed braze assembly 855 afterthreading, and other inner components 860 of a microstimulator housedand stabilized in an assembly carrier 861. The u-loop 859 protrudes froma groove 863 of the carrier 861. The u-loop 859 may be secured by awedge 862 that pivots and is placed upon the u-loop 859. An elevatorscrew 864 is tightened in order to raise the inner components 860 untilthe top surface of a capacitor 865 of the inner components 860 touchesthe bottom surface of the u-loop 859. The u-loop 859 may be anothershape that permits the u-loop 859 to come into maximum contact with thecapacitor 865. Likewise, the components and the carrier 861 of FIG. 12may be arranged in a variety of different manners so as to permit theu-loop 859 to come into maximum contact with the capacitor. Conductiveepoxy, solder, or other similar material or method is used to create apermanent electrical connection between the u-loop 859 and the capacitor865. The excess end of the wire 856 of u-loop 859 is removed.

FIG. 13 is a perspective view of a microstimulator 870 before finalassembly. The wire 856 and the capacitor 865 are electrically attachedto each other. The case 213 and the braze assembly 855 can now be slidover the body of the inner components 860. After the braze assembly 855is slid over the inner components 860, the elbow 858 end of the wire 856remains, exiting from the electrode 857.

FIG. 14 is a perspective view of a pre-assembled microstimulator 870horizontally housed and secured in an assembly carrier 871. Aspring-loaded base 872 compresses the microstimulator against the wall873 of the carrier 871 so that the case 213 and the braze assembly 855are firmly held together. The case 213 is then laser spot welded, orotherwise attached, to the braze assembly 855 at union 874. Themicrostimulator 870 is then rotated in the carrier 871 and the union 874is spot welded, or otherwise attached, at other points along thecircumference of the union 874. The microstimulator 870 is then removedfrom a horizontal position in the carrier 871 and placed into verticalposition within a hole 875 in the carrier 871 and oriented with theelectrode 857 and wire 856 exiting the hole 875, as shown in FIG. 15.

FIG. 15 is a perspective view of the microstimulator 870 verticallyhoused in the carrier 871. The wire 856 is laser spot welded, orotherwise electrically attached, to the electrode 857, resulting in anelectrical connection between the electrode 857 and the capacitor 865(FIG. 13). During the laser weld process, the excess wire 856 is cut andremoved from the microstimulator 870. If the wire 856 is otherwiseelectrically attached to the electrode 857, the excess wire 856 is cutor otherwise removed in a manner consistent with the respectiveapproach. Before the wire 856 is attached and removed, a preferred andappropriate amount of slack may be provided to the wire 856 in order toavoid wire disconnection during any thermal expansion of themicrostimulator 870.

FIG. 16 is a perspective view of a microstimulator 870 after finalassembly. The microstimulator 870 has been laser welded, or otherwisepermanently attached, along the entire circumference of union 874. Themicrostimulator 870 shown in FIG. 16 has been brazed, welded, and coatedaccording to the teachings of the present invention.

The feed-through hole design and method of FIGS. 11 to 16 is animprovement upon other structures and methods used to electricallyattach an electrode to the inner components of a hermetically-sealedmicrostimulator. The feed-through hole design and method of the presentinvention is a positive, mechanical connection that is completed after acase of a microstimulator is completely assembled, rather than before.By welding a wire to the electrode of the microstimulator after the caseof the microstimulator is completely assembled, the electricalconnection formed using the wire does not risk disconnection during awelding or brazing process. A welding or brazing process is likely tocreate thermal expansion, contraction, and mismatch of the differentmaterials of the case, because the different materials have differentthermal coefficients. Further, by welding a wire to the electrode of themicrostimulator after the case of the microstimulator is completelyassembled, a preferred and appropriate amount of slack may be providedto the wire in order to avoid wire disconnection during any futurethermal expansion of the materials of the microstimulator.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

1. A braze assembly, comprising: a first metal member including anexterior flange of the first metal member, the exterior flange includingan inner surface; a braze material including titanium and nickel; and aceramic member including a formed end, wherein the formed end of theceramic member adjoins the inner surface of the exterior flange and isbrazed to the first metal member with the braze material, wherein theceramic member is a substantially close-ended ceramic can and includes asecond metal member which forms an end cap to the ceramic member, whichend cap completely closes the end of the ceramic can, wherein the endcap is an electrode, and wherein the electrode further comprises: anarrow-diameter pin; a broad-diameter braze surface adjoining thesubstantially closed-end of the ceramic member; and a stimulatingsurface with grooves that increase the surface area of the stimulatingsurface.
 2. The braze assembly of claim 1 wherein the braze assembly isused to hermetically seal the shell of a microstimulator.
 3. The brazeassembly of claim 1 wherein the exterior flange forms a step at the endof the first metal member against which the formed end of the ceramicmember may be received, and wherein the surface area between the firstmetal member and the ceramic member is capable of receiving an adequateamount of braze material to form a strong braze bond.
 4. The brazeassembly of claim 3 wherein the exterior flange provides lateral supportto the braze assembly.
 5. A braze assembly for a microstimulator,comprising: a first metal member including an exterior flange of thefirst metal member, the exterior flange including an inner surface; abraze material including titanium and nickel; and a ceramic memberincluding a formed end, wherein the formed end of the ceramic memberadjoins the inner surface of the exterior flange and is brazed to thefirst metal member with the braze material; wherein the ceramic memberis a substantially close-ended ceramic can and a second metal memberforms an end cap to the ceramic member, which end cap completely closesthe end of the ceramic can, wherein the end cap is an electrode, andwherein the electrode further comprises: a narrow-diameter pin; abroad-diameter braze surface adjoining the substantially closed-end ofthe ceramic member; and a stimulating surface with grooves that increasethe surface area of the stimulating surface; and wherein the first metalmember, the braze material, and the ceramic member form a braze assemblythat is used to hermetically seal a microstimulator shell.
 6. The brazeassembly of claim 5 wherein the exterior flange forms a step at the endof the first metal member against which the formed end of the ceramicmember may be received, and wherein the surface area between the firstmetal member and the ceramic member is capable of receiving an adequateamount of braze material to form a strong braze bond.
 7. The brazeassembly of claim 6 wherein the exterior flange provides lateral supportto the braze assembly.
 8. A braze assembly, comprising: a first metalmember including an exterior flange of the first metal member, theexterior flange including an inner surface; a braze material includingtitanium and nickel; and a ceramic member including a formed end,wherein the formed end of the ceramic member adjoins the inner surfaceof the exterior flange and is brazed to the first metal member with thebraze material, wherein the ceramic member is a substantiallyclose-ended ceramic can and includes a second metal member which formsan end cap to the ceramic member, which end cap completely closes theend of the ceramic can, wherein the end cap is an electrode, and whereinthe electrode further comprises: a stimulating surface with grooves thatincrease the surface area of the stimulating surface.
 9. The brazeassembly of claim 8 wherein the braze assembly is used to hermeticallyseal the shell of a microstimulator.
 10. The braze assembly of claim 8wherein the exterior flange forms a step at the end of the first metalmember against which the formed end of the ceramic member may bereceived, and wherein the surface area between the first metal memberand the ceramic member is capable of receiving an adequate amount ofbraze material to form a strong braze bond.
 11. The braze assembly ofclaim 10 wherein the exterior flange provides lateral support to thebraze assembly.
 12. A braze assembly for a microstimulator, comprising:a first metal member including an exterior flange of the first metalmember, the exterior flange including an inner surface; a braze materialincluding titanium and nickel; and a ceramic member including a formedend, wherein the formed end of the ceramic member adjoins the innersurface of the exterior flange and is brazed to the first metal memberwith the braze material; wherein the ceramic member is a substantiallyclose-ended ceramic can and a second metal member forms an end cap tothe ceramic member, which end cap completely closes the end of theceramic can, wherein the end cap is an electrode, and wherein theelectrode further comprises a stimulating surface with grooves thatincrease the surface area of the stimulating surface; and wherein thefirst metal member, the braze material, and the ceramic member form abraze assembly that is used to hermetically seal a microstimulatorshell.
 13. The braze assembly of claim 12 wherein the exterior flangeforms a step at the end of the first metal member against which theformed end of the ceramic member may be received, and wherein thesurface area between the first metal member and the ceramic member iscapable of receiving an adequate amount of braze material to form astrong braze bond.
 14. The braze assembly of claim 13 wherein theexterior flange provides lateral support to the braze assembly.